Analysis of treatment protocols using azithromycin eye drops for bacterial blepharitis: second report-bacteriological investigation.

Purpose: To gain new insights into the etiology of blepharitis, we investigated the causative bacteria in patients with blepharitis and the effects of 1% azithromycin ophthalmic solution.

Study Design: A multicenter, prospective observational study.

Methods: After the subjects were diagnosed as having blepharitis they were administered 1% azithromycin ophthalmic solution for up to 14 days. Bacterial cultures and smear microscopic examinations of the eyelid margin were conducted at the initial visit, after administering eye drops, and 1 month after the end of eye drop administration. The minimum inhibitory concentrations (MICs) of azithromycin were measured.

Results: At the initial visit, the bacterial morphology determined by smear microscopic examinations coincided with that of strains isolated by culture taken from 22 of 45 patients. All detected bacteria were gram-positive, and Corynebacterium spp., Cutibacterium acnes, Staphylococcus epidermidis, Streptococcus spp., and Enterococcus faecalis were isolated most commonly. Compared with the initial visit the number of isolated strains per eye decreased significantly at 7 days after the start of eye drop administration and 1 month after the end of eye drop administration. The azithromycin MICs were temporarily increased after the start of eye drops but then decreased.

Conclusion: Our study suggests that in blepharitis pathogenicity is characterized by increased strain numbers and amounts of indigenous bacteria. Administering a 1% azithromycin ophthalmic solution suppresses the number of bacterial strains within 1 month after the end of eye drop administration without increasing drug resistance.